Ion sources, such as so-called gridless ion sources of the end-Hall-type, are used to produce ion beams for use, for instance, with sputtering targets or the like to deposit thin films on articles located within high vacuum coating chambers. An example of an end-Hall ion source is disclosed by U.S. Pat. No. 4,862,032 issued to Kaufman et al. Such an ion source typically includes an anode and cathode between which a potential is impressed to produce a flow of electrons. A magnetic field is established between the anode and cathode to define the path of the electrons, and a distributor plate is used to direct a flow of working gas to the anode and cathode so that the electrons bombard and collide with the neutral atoms or molecules of the working gas to create a conductive gas or plasma.
As disclosed by the Kaufman '032 patent on column 3, lines 64–67, column 8, lines 54–55, and column 9, lines 34–54, such an ion source requires routine maintenance including cleaning and replacement of eroded parts. For example, the gas distributor plate erodes during normal operation since it is repeatedly struck by energetic ions. Most of the erosion of the gas distributor plate occurs at the center of the plate that faces the central opening of the annular anode. Replacement of the gas distributor plate prevents the erosion from creating an undesired hole in the center of the gas distributor plate and reduces contamination of the target. From a practical standpoint, it has been determined that a gas distributor should be replaced when its thickness at an eroded central location is reduced to approximately half of its original thickness. Thus, maintenance of such an ion source includes periodic dimensional measurement of the erosion depth of the gas distributor.
Measurement of the erosion depth of a gas distributor plate, which is typically located within the housing of an ion source assembly, is difficult to accurately perform when the ion source is assembled. Thus, this measurement can only accurately be determined when the ion source is disassembled, which is typically only performed when the ion source is due for a thorough cleaning. Of course, disassembly of the ion source is also required to replace the gas distributor.
FIGS. 1–7 provide an example of the steps required to disassemble a gridless ion source. An assembled gridless ion source 10 is shown in FIG. 1. Typically, the ion source 10 is mounted to a support bracket (not shown) via a socket 12 shown in FIG. 2. Thus, the ion source 10 must be disconnected from the socket 12, and then the cathode 14 and cathode supports 16 are removed as shown in FIG. 3. The front support plate 18 is removed followed by the outer shell 20 as illustrated in FIG. 4. The front anode support 22 is then removed followed by the anode 24 and rear anode support 26 as illustrated in FIGS. 5 and 6. Thereafter, the gas distributor 28 is removed as shown in FIG. 7 so that the extent of erosion at its center can be measured. If the amount of erosion is within acceptable limits the gas distributor 28 is re-installed. If not, a new gas distributor is installed. The time required to perform the above tasks typically requires about one hour of labor and is required to be performed more frequently than scheduled thorough cleanings of the ion source.
While the ion source, gas distributor, and maintenance procedures disclosed above may be satisfactorily for their intended purposes, there is a need for a gas distributor, ion source, and maintenance procedure therefor that permit ready and precise inspection of an eroded surface area of a gas distributor and that simplifies the steps required to place an ion source into an in-service condition with a gas distributor having desired surface qualities. To this end, the required labor and downtime of the ion source should be reduced, the material costs related to providing a distributor plate with a desired surface should be reduced, and accurate erosion measurements should be capable of being readily taken at frequent intervals within a minimum of time and requiring only a minimum of skills.